Mobile excavation machines such as dozers, agricultural tractors, and scrapers often include one or more material engaging implements utilized to cultivate, dig, rip or otherwise disturb a ground surface. The ground surface can include non-homogenous loose soil or compacted material that can be easy or difficult for a machine to process. As a machines traverses a site that has changing terrain and/or varying ground surface conditions, the magnitude of resistance applied by the material to the implements and to traction devices of the machine also varies. If not accounted for properly by an operator of the machine, the machine can quickly be overloaded or underloaded. When the machine is overloaded, the traction devices of the machine can be caused to slip (i.e., spin faster than a travel speed of the machine), thereby reducing a forward momentum of the machine and possibly damaging the machine. The loss in momentum can result in lost productivity and/or efficiency. When the machine is underloaded, although the traction devices may not slip, the machine may still lose productivity and efficiency due to a reduced volume of material being moved. In order to help ensure that high productivity and efficiency of the machine are attained without damaging the machine, the operator of the machine must continuously alter settings of the machine and implement to accommodate the changing terrain and ground surface conditions. This continuous altering can be tiring for even a skilled operator and difficult, if not impossible, for a novice operator to achieve optimally.
Traditionally, slip of a mobile machine has been addressed by determining that slip is occurring in one of the traction devices and then manually or autonomously reducing a torque applied to the one or all of the driven traction devices (e.g., by raising or lowering the machine's implement). Although adequate for some situations, this method of reducing slip may still be problematic. In particular, slip must still occur before any action is taken to reduce the slip, thereby still allowing for some loss in productive and efficiency and/or for some damage to occur.
An alternative method of accommodating slip while trying to improve productivity and efficiency is described in U.S. Pat. No. 6,666,279 of Scarlett et al. that issued on Dec. 23, 2003 (“the '279 patent”). In particular, the '279 patent describes a control apparatus that determines an optimal pull-slip curve for use in controlling an associated tractor/implement combination. During a calibration period, the control apparatus records multiple reference values for wheel slip and engine torque corresponding to different depths of an implement pulled by a tractor. The control apparatus then selects one of a series of stored pull-slip curves that most closely approximates the recorded reference values. The selected pull-slip curve is subsequently used in a control algorithm that attempts to reduce slip by limiting engine torque before significant slip occurs.
While the method of the '279 patent may improve machine performance, it may still be less than optimal. Specifically, the calibration process required at startup of the tractor/implement combination, prior to selection of the stored pull-slip curve, may be cumbersome and time-consuming to implement. In addition, because ground conditions can change dramatically within a small work area and/or within a short period of time, the selected curve may not be functional for long. Accordingly, additional calibration processes may be required during a single work shift. Further, the stored pull-slip curves may be theoretically and/or analytically developed and, thus, may not closely match actual performances of individual machines.
The disclosed drive system is directed towards overcoming one or more of the problems as set forth above and/or other problems of the prior art.